Stabilized solutions of acrylonitrile polymers and stabilized solvent



Patented June 16, 1953 STABILIZED SOLUTIONS OF AoRYLoNI- TRILE POLYMERS ANDSTABILIZED SOLVENT Theodore E. Stanin and Joseph B. Dickey, Rochester, N. Y., and Harry W.' Coover, Kingsport,

, Tenn assignors to Eastman Kodak Company; Rochester, N. Y., a corporation of New Jersey 7 Serial No. 156,234

v No Drawing. Application April 15,1950,

6 Claims. (O1. 260+325) This invention relates to tabilized "solutions of acrylonitrile polymers; and to a stabilized solvent for these polymers.

' This application is a continuation-in-part of our copending applications Serial No. 49,651, Serial No. 49,652, and Serial No. 49,653, all filed September 16, 1948. Serial No. 49,651 issued as U. S. Patent 2,629,711 on February 24, 1953, and Serial'No. 49,652 issued as U. S. Patent 2,629,712 on the same date.

It is known that solutions of polymers of acrylonitrile can be prepared by dissolving such polymers in various organic solvents or inaqueous solutions of certain inorganic metal salts. These solutions have been found to be readily adaptable for spinning into fibersor in themanuiacture of film. Since the metal salts have a tendency to deposit on the filaments during the Spinning operation, and removal thereof during the passage of the filaments through the spinning bath leaves numerous voids or weak spots in the fibers,-metal salts have not proved to be entirely satisfactory in the preparation of synthetic fibers. .Difiiculties are also encountered when organic solvents are used in the spinning of fibers from solutions of polymers of acrylonitrile. Yet particles .frequently form, thus either clogging the spinnerets Or giving a fiber of low tensile strength. Also the color of the fibers spun from many of the solvents heretofore used does not meet the standards demanded of a product in a competitive market. V I

Houtz U. S. Patent 2,404,713, dated July 23, 1946 and Latham U. S. Patent 2,404,714 dated July 23, 1946, describe processesior preparing solutions of polymers of acrylonitrile suitable for spinning into fibers which comprises dissolving the polymer in an organic compound containa V 0 H CH:

Jl-N

CHI group e. g, N,N-dimethylformamide. These 301- vents provide a convenient medium irom whichfibers can be spun, however there is some tendency for the polymers containing acrylonitrile to ball or form large. gel particles therein. To overcome this difficulty, it has been proposed to add gaseous anhydrides to the cooled Solvent containing'the polymer to obtain a uniform dispersion of the polymer in the vehicle, and then gradually warm the dispersion to a temperature of'l00-130;C., while solution is effected and the gaseous anhydride is expelled from the solu'-" the benzeneseries).

ionic acids include naphthalene a sulionic,

tion (Finzel 'U. s. Patent 2,404,728, dated July It is an object of thisinvention to provide Stabilized solutions of polymers of acrylonitrile which aresubstantially clear, colorless, and gelfree.

Another object is to taining these solutions. p

Still another object is to provide a stabilized solvent for polymers of acrylonitrile.

A further object is to provide white, lustrous fibers from such solutions and a process for preparing such fibers. .Other objects will become apparent from a consideration of the following provide a method for obdescription and examples.

The above objects are directed to the stabilization of solutions of polymers of acrylonitrile in N,N-'dimethylacetamide, and to the stabilization of the N,N-diniethylacetamide.

According to our invention we accomplish the above objects by intermixing or commingling a polymer of acrylonitrile containing in the polymer molecule at least 80 per cent by weight of acrylonitrile with .N,N-Idimethylacetamide containing certain inorganic or organic acids, or anhydrides. These inorganic or organic acids,

or anhydrides, stabilize thev N,N- dim'ethylacet-,

phosphorous acids, alkane'phosphonic acids and allrene sulfonic acids. Typical, alkane sulfonic. acids include methanesulfonic, ethanesulfonic, propane-l-sulfonic, propaneLQ-su'lfonic, n-butane-l-sulfonic, isobutane-l-sulfonic, sulfoace fl tic, p hydroxy-ethylsulionic, etc. acids (c.gl alkane sulfonic acids containing from lfto'4 carbon'atoms), Typical aromatic sulionicacids in clude benzenesulfonic, 'p -toluenesulfonic,' otoluenesulfonic, m-benzenedisulfonic, 1,3,5-benzenetrisulfonic, etc. acids (e. g. a sulfonic acid of Other useful. aromatic sul naphthalene fi-sulfonic, 1,5 g naphthalenedisulionic, 2,6-naphthalenedisulionic, etc; acids (e.

g; a sulfonic acid of the naphthalene series),

- ypic al yl p phoric acids include 'mono methyl acid orthophosphate, monoethyl acid orthophosphate, mono-n-propyl acid orthophosphate, monoisopropyl acid orthophosphate, inono-n-butyl acid orthophosphate, monoisoamyl acid orthophosphate, mono-n-octyl acid orthophosphate, mono-n-capryl acid orthophosphate, dimethyl acid orthophosphate, diethyl acid orthophosphate, ethyl isoamyl acid ortho phosphate, ethyl n-octyl acid orthophosphate, ethyl 'n-capryl acid orthophosphate; di n-butyl acid orthophosphate, n-butyl 'n-amyl acid or thophosphate, dimethyl acid pyrophosphate, diethyl acid pyrophosphate, di i'i-propyl acid pyrophosphate, diisopropyl acid pyrophosphate, di-'- n-butyl acid pyrophosphate,.diisoainylacid pyrophosphate, di-n-octyl acid pyrophosphate, dih-capryl acid pyrophosphate, etc. "(See- Alder 82 Woodstock Chem. Ind, vol II (1942) 5L6.) Typical alkyl phosphorous acids include: mono: methyl acid phosphite, monoethyl acid phosphite, mono-n-propyl acid phosphite, monoisopropyl acid phosphite, 'monoisobutyl acid phosphite, monoisoamyl acid phosphite j dirnethyl as r o shita dicjthyr ac .pho phi e; dim.-

propyl' acid phosphite; diisopropyl acid phos- 2 phi-te, di-n-butyl acid phosphite, diisobutyl' acid phosphite, monoethyl acid hypophosphite, monoi'sobutyl acid hypophosphite; etc; Alky lphosphoric and phosphorous acid (i. e. allgyl: acid esters of acids ciphosphorus) containing from 1 to. ill carbon atoms in the alkyl group, have been foundto be especially useful. Alkylj, acid esters of: acidsof phosphorus containing from 1 to 5" atoms in the alkyl? group constitute a preferred class. Typical alkane phosphonic acids include methane phosphonic, ethane phosphonic, n-propane phosphonic; isobutane phosphonic (isobutyl phosphonic);isopentane phosphonic (isoamyl phosphonicl etc, acids (e. g. alkane phosphonic acids containing from 1' to 5 carbon atoms). Typical alkene phosphonic acids include: vinyl phosphonic, propene-Z-phosphonic, a-phenylvinyl phosphonic, etc. acids (e; g, an h-unsaturated, alkene phosphonic acid containing from 2' .to 8 carbon atoms, in the alkene group); Alkenephosphoni'c acidsusefiil in practicinglour invention are desoribedfinUI S. Patent 2365;466", dated December 19; 1944; The advantages obtained with. one or more. or the above acids donotext'end to organic acidgeneijally we have, found. Forv example, succinic, adipic, trichloroacetic; propionic, etc. acids do not provide the mcrdvemems which havebeen observed when the acids. enumerated aboveare used.

As inorganic acidswecan use the oxygenacids of phosphorus (i, e. ineta'phosphoric, OIfthODhOS- phoric, hypophosphoric, p'yrophosphoric; metaphosphorous orthophosphorous, hypophosphorous or pyrophosphorous acid). As anhydlides We can advantageously use those of the oxygen acids of phosphorus ie. oxidesof,- phosphorus, such as phQSDhorusi trioxide (P2Qs) ph0sphorus tetraoxide (P204). and. phosphorus; pentoxide (B205). The,.advantages .obtained withaone or; moreoftheabove acids or oxides of phosphorus donot extendto inorganicacidsor anhydrides generally, we have found. For example, the. hydrohalogen acids (e. g. hydrochloric, hydrobromic, etc. acids); nitric acidrpersulfuricacid, etc., do not provide the. improvements which we have obtainedwith our new, solutions. of polymers of acrylonitrile.

The quantity ofacidor anhydrideused varies and'is generally a functl'onloflthe.particulanaoid 4 or anhydride employed. For the purposes of our invention we have found that from 0.1 to 5.0 per cent by weight, based on the weight of solvent, of acid (or anhydride) is adequate. Larger or smaller quantities of acid (or anhydride) can be used, although there is ordinarily no advantage in using amounts other than those indicated above.

Instead of employing the acids themselves in our process, we can form the acid in situ, as for example, by adding an anhydride of the acid to the solvent. Since the solvent generally contains a small amount of water, the water reacts with the anhydride to form the free acid. This method of procedure also serves as a convenient means for dehydrating the solvent and increasing the dissolving power of the solvent for the polymer. The term acid as used in the following description is intended to define both the free acid and its anhydride.

Advantageously we canv effect solution of the polymers of acrylonitrile by applying a small amount of heat to the mixture of the acid, polymers and solvent. Since the acids used in our invention increase the dissolving power of the solvents to such a marked degree, it is not essential that the mixture be heated. Heat doesserve to shorten the time required to efiect solution. Care should be taken not to heat the mixture for prolonged periods of time, since heating lowers the color characteristics of fibers spun from heated solutions. The effect of prolonged heating on the solutions obtained according to the process of our invention is not as. deleterious as that which results when solutions containing no acid are'so heated. In order to obtain uniform solutions according to methods heretofore employed, the dispersion of polymer has to be subjected to high temperatures for a time. This heating caused a diminution in desirable color properties in the solution, which are passed along during the spinning to the fibers formed. This heating can be largely or entirely avoided in our invention, however, thus providing, fibers which are white and lustrous.

The inorganic gas'eo'usl anhydrides. previously added to N,N-dimethylformamide were for. the purpose of reducing; the dissolving. power of this solvent forthe polymers of'acrylonit'rile, so that adispersion could'be obtained. The acids (or anhydrides) used in this invention arein contradistinction thereto for the purpose of increasing this dissolving power of thesolvent for. the polymer. Whereas the. polymers used'accordi'ngto the older, less eih'cacious methods had to be ground to minute particle size, the polymer used in this invention can be ZO-meshsize or larger, with little. or no apparent ftencle'ncy to-ballingf or the formation of gel particles. The solutions obtained in our invention are more stable than those obtained heretofore and show less tendency to gel, or develop color-on standing.

The amount of polymer dispersed in the solvent can be varied dependingionthe intended use of the polymer solution and the-molecular weight of'the polymergii. e: larger quantities oflowermolecular weight polymers must be added to give a viscosity comparable-to that obtained with a given amount. of. a higher. molecularweight polymer. Although. our invention is not to be limited thereby, generally; oursolutionscan. contain from about .2 to. 25v per. cent-by, weight of the polymer, .basedon the weight of the-solvent.

v The molecular. weihhof the :polymers used. herein. vary from. about 50,000 to -500;0O0;=

although polymers having a molecular weight as low as 25,000 or as high as 750,000 can be used to advantage.

In our applications Ser. No. 49,651, Ser. No. 49,652, Ser. No. 49,653, all filed on September 16, 1948, we have described methods for preparing polymers of acrylonitrile having improved solufrom polymers prepared according to prior art.

7 yield of polymer methods, we have found that the present invention provides solutions of polymers of acrylonitrile, and fibers prepared therefrom, having even more markedly improved properties when the solutions and fibers prepared according to the process described herein are obtained from polymers of acrylonitrile prepared according to the processes described in our applications Ser. No. 49,651, Ser. No. 49,652 and Ser. No. 49,653. That is to say, by applying the improved process of this invention to the improved methods for preparing polymers of acrylonitrile, described in our copending applications, solutions and fibers of polymers of acrylonitrile of particularly outstanding properties can be obtained.

The following examples will illustrate more fully the manner whereby we practice our invention.

EXAMPLE 1 20 g. of freshly distilled acrylonitrile were added to 200 cc. of distilled water containing 1.1 cc. of sulfuric acid (s. g. 1.84) in a 240 cc. screw-cap bottle. The mixture was thoroughly shaken until the water was saturated with monomer. To this solution were added 0.8 g. of sodium bisulfite and 0.4 g. of ammonium persulfate, the cap screwed on tightly and the mixture shaken again. The bottle was placed on a tumbling wheel which revolved at five revolutions per minute and. tumbled at room temperature for 18 hours. The polymer was thenfiltered off, washed thoroughly with distilled water and dried- The yield was 18.8 g. of pure white powder.

EXAMPLE 2 20 g. of acrylonitrile were polymerized according to the method set forth in Example 1 above, except that 1.4 cc. of concentrated nitric acid were employed in place of the sulfuric acid. After drying, the yield of polymer 18.9 g.

EXAMPLE 3 After drying theyield of polymer'was 19.6 g.

EXAMPLE i 20 g. of acrylonitrile were polymerized according to the method set forth in Example 1 above, except that 1.2 cc. offormic acid were employed in place' of the sulfuric acid. After drying, the

was 18.8 g. EXAMPLE 5 20 g, ofacrylonitrile were polymerized according to the method set forth in Example 1 above, except that 1.38 cc. of glacial acetic acid were used in place of the sulfuric acid. After drying,

the yield of polymer was 18.6 g.

Solutions of the acrylonitrile polymers obtained in the aboveexamples were prepared by dispersing 1.0 g. of the polymer in 20 cc. of N,N-dimethylacetamide, adding'0.5 per cent of phosphorus pentoxide, and stirring untilsolution. was effected. To detect the stabilizing effect of the phosphorus pentoxide the solutions were heated at 100 C. for the periods of time indicated in 1 the table below, and the blue light transmission j of the solutions measured as a means of determining the extent of solution and detection of any discoloration present, since blue light was more highly absorbed in a discolored solution than the other colors of the spectrum. The results are given in the following table:-

" Table I Blue Light Transmission- Solution from Percent Stabilizing Polymer of Agent Example 1 D H0119 P205 none P 05 none P205 The above measurements were all based on the transmission of pure N ,N-dimethylacetamide which was set at 100 per cent.' It can thus be seen that the addition of a small amount of phosphorus pentoxide produces a beneficial effect upon the polymer solutions. While the blue light transmission of the solutions containing no phosphorus pentoxide washigh after only five minutes heating, at the end of one hours heating at 100 0. not one of the unstabilized solutions had a blue light transmission as high as per cent while the lowest blue light transmission for the stabilized solutions was 90 per cent. The heating accelerates the discoloration of the unstabilized solutions to a marked degree, while having little effect on the stabilized solutions. The effect of heating illustrates what can be expected in the spinning of fibers from the solutions, or upon prolonged storage thereof. A limited amount of heating has a beneficial effect, while prolonged heating has the discoloration eiTect-shown above.

Heating also causes the solutions containing no added acid or. anhydride to gel in a relatively short period of time as shown in the following table. Since heat is generally used-to shorten the time required to efi'ect solution of the polymers, it can be seen that the disadvantages caused through the use of heat present a formidable problem in the spinning operation of solutions of polymers into fibers, because of the accelerated formation of gel particles, and theobtention of white, lustrous-fibers from solutions subjected to the influences of heat. Solutions of the polymers obtained in the ,above' examples were prepared byrlispersing [1.0, g. of the polymer in 7 321) cc. of NN-dimethyacetamide adding 015' per cent of phosphorus' pentoi ii'de and stirring at room temperature until solution was effected. The solutions were then heated at 120 C. and the time required for the solutionrto gel was observed. Theobservedtime i's-given'in the following tableas gel-time.

' Table-II 1 The values givcn are not absolute,due tostheecceptrlcityof the polymer solutions, the gelling "iimes varying slightly from one batch-oi polymer to another.

From the data given it :cegnbe-seen that the presence of phosphorus-..pentoxide in the solution i 7 serves to stabilize the solution against gelling to an extent not heretofore obtainable.

In a manner similar to that illustrated .above, solutions of the acrylonitrile polymers obtained in Examples 1 to 5 were prepared by dispersing 1.0 g; of the polymer in .20 cc. of-N,N-dimethyl acetamide, adding L percent of the acids listed below (-basedon the weight of the imN-dimethylacetamide), and stirring until solution was e'f- "fected. The blueilight transmission of the solutions'vvas then measured as a means of determiningthe extent of solution and detection of any irregularities .ipresent. The lnieasurements were based on the blue light transmission ofpure N,N-dimethylacetamide which was set at lOOper cent. The results are given in the follow-ing table.

Table III p Blue Light lranem ls'slon- Percent Solution cffi Polymer l M y o 1 w Acid Acid; Acid; Acid :A c1d Control A C D E "Example 1 "89 i9? osf off 99 95 Example 2... 81 96 -94 :96 97 93 Example 3 --87 :25 {.94 96.- 95 94 Example 4...- 58B 95 93' 95 96. 93 -Example 5 J 86 94 92 =94 95' 92 Acid A=ortl1ophosplioiic and. Acid B =ethanesulionio. acid.

Acid C=oxalic acid.

Acid D=trifluoroaetic acii Acid E=ethanephosphonlc acid.

While immediate improvementzc'ambe observed due to the addition'of the above 'acids (or anhydrides) as shown -by the data inlTable l the improvement becomes more .marked'ias the-solutions areaged. Asshow'n by Table-ill, the acids or anhydrides :"stabilize the -polymer solutions against undesirable gelling, whichrwould aprevent utilization of the solutions in the spinning :of

fibers.

By replacing-the oxalic'acid used in Table III with a molecularly tequivalentiam'ount of acetic anhydride, a solution which is stable to long periods of heating "can he :obtained.

In a manner similar to .thatiillustratedother acids or anhydride's selected from'those setaforth above can be employed to advantage. :For ex- -'ample, the ethanesulfonic acid in TabIe-III can acetamide. a small part, however, since such small amounts .;be replaced by molecular-1y quivalent amounts :7

E01 aromatic sulfoni'c acids (e. g. benzenesul'fonic acid, p-toluen'esulfonic acid, etc.) to give useful solutions of polymers of acrylonitrile. In like manner the ethanephosphonic acid can be replaced by molecularly equivalent amounts of alkyl acid esters of acids of phosphorus (a g. monomethy-l acid phosphite, diethyl acid phosph-ite, diisobutylacid phosphite, etc.).

Although our invention has been found to be especially useful in the preparation of solutions of the homopolymer of acrylonitrile, solutions of interpolymers of acrylonitrile with other interpolymerizable compounds, e. g. acrylic acid, acrylamide, ethyl acrylate, vinyl acetate, vinyl -'chloride, styrene, etc. can also be prepared. The interpoly-mers used should generally contain at least '80 per cent by weight of acrylonitrile in thep'oly-mer molecule, since polymers containing less than this amount melt at too low temperatures to warrant their use in the preparation of commercial products, such as fibers or yarns. Generally from 6 to 9 per cent by Weight of the other polymerizable material in the interpol-ymer is adequate for the purposes'of our invention. Interpolymers containing less than 80 per cent by weight of acrylonitrile in the polymer molecule '(e. g. from to per cent) also can be advantageously utilized in the preparation of our polymer solution. These interpolyiners are useiu'l where an unusually high melting polymer is not required, as for example, in the preparation of films or sheets.

Although the reasons for the unexpected behavior-and properties of the solutions of our invention are not fully understood, it appears that, at least in part, these phenomena are associated with areduction in alkalinity of the solvent. 'lwl-ydi'ocyanic acid is apparently released from the polymer under strongly alkaline conditions thus causing discoloration of the solutions. The-stabilizing efiect of the above acids or anhydrides on N,N-dimethylacetamide, and solutions of polymers therein, also appears in part to 'be due to a reduction of free amine in the N;N-dimethyl- Salt formation appears to play only of acids or anhydride-s stabilize effectively. The amount of acids, or anhydrides, added are not generally suflicient to neutralize all free amine and also form acid-addition salts With the large :amount of amide present. Small amounts of :acid, or-anhydride, cause a marked lowering in ?the pH of the amide, and this lowering is in some manner associated with the stabilization effect observed. The acid, or anhydride, arrests the alkalinity of the N,N-dimethylacetamide, which would progressively increase in the ab- Sence of the stabilizing agent.

This increase in alkalinity'on standing renders the *N,N-dimethylacetamide a poor solvent :for :polymers which are readily hydrolyzed, such-as polyvinyl iorinate, polyvinyl acetate, polyvinyl trifiuoroacetate, etc. Solutions ofthesepolymers in the amide undergo hydrolysis with the formation of insoluble polyvinyl alcohol, which precipitates .out. The unstabilized solvent is -.'thus of little value from'a practical standpoint in the preparationof spinning or coating solutions-from these-polymers.

N,N-dimethylacetamide which has been stabilized with a small amount of the above acids or anhydrides is entirely satisfactory as a solvent forthese easily'hydrolyzed polyvinyl esters, since no separation -:of insoluble polyvinyl alcohol is apparent after prolonged storage.

While the pH of N,N-dimethylacetamide varies from 8.6 to 9.2, or even higher as aging progrosses, we have noted that as small an amount as 0.5 per cent of phosphorus pentoxide reduces the pH to about 3.0 and prevents the pH from rising substantially higher than this figure. As noted above, the advantages of our. invention have not been found to extend to all acids; or anhydrides. Because of this fact, the simple reduction in pH of the N,N-dimethylacetamide does not explain all of the phenomena of our invention.

What we claim as our invention and desire secured by Letters Patent of the United States is:

1. As a new composition of matter, a stabilized solution of a polymer of acrylonitrile, containing in the polymer molecule at least 80 per cent by weight of acrylonitrile, in N,N-dimethylaceta mide, said solution containing from 0.1 to 5.0 per cent by weight, based on the weight of the N,N- dimethylacetamide, ofan inorganic oxygen acid of phosphorus.

2. As a new composition of matter, a stabilized solution of a polymer of acrylonitrile, containing in the polymer molecule at least 80 per cent by weight of acrylonitrile, in N,N-dimethylacetamide, said solution containing from 0.1 to 5.0 per cent by Weight, based on the Weight of the N,N- dimethylacetamide, of orthophosphoric acid.

3. As a new composition of matter, a tabilized solution of a homopolymer of acrylonitrile in N,N-dimethylacetamide, said solution containing from 0.1 to 5.0 percent by weight, based on the weight of the N,N'-dimethylacetamide, of an inorganic oxygen acid of phosphorus.

10 4. As a new composition of matter, a stabilized solution of a homopolymer of acrylonitrile in N,N-dimethylacetamide, said solution containing from 0.1 to 5.0 per cent by weight, based on the weight of the N,Ndimethylacetamide, of orthophosphoric acid. 5. As a new composition of matter, a stabilized solution of a polymer of acrylonitrile, containing in the polymer molecule at least 80 per cent'by weight of acrylonitrile, in N,N-dimethylaoetamide, said solution containing from 0.1 to 5.0 per cent by weight, based on the weight of the N,N-

dimethylacetamide, of hypophosphorous acidli 6. As a new composition of matter, a stabilized solution of a homopolymer of .acrylonitrile in N,N-dimethylacetamide, said solution containing from 0.1 to 5.0 per cent by weight, based on the weight of the N,-N-dimethylacetamide, of hypo-" phosphorous acid.

DAlelio NOV. 28. 1950 

1. AS A NEW COMPOSITION OF MATTER, A STABILIZED SOLUTION OF A POLYMER OF ACRYLONITRILE, CONTAINING IN THE POLYMER MOLECULE AT LEAST 80 PER CENT BY WEIGHT OF ACRYLONITRILE, IN N,N-DIMETHYLACETAMIDE, SAID SOLUTION CONTAINING FROM 0.1 TO 5.0 PER CENT BY WEIGHT, BASED ON THE WEIGHT OF THE N,NDIMETHYLACETAMIDE, OF AN INORGANIC OXYGEN ACID OF PHOSPHORUS. CONSISTING IN FIRST FORMING A PLURALITY OF COMPONENT STRANDS BY COMBINING FOR EACH STRAND A PLURALITY OF CRIMPED INDIVIDUAL FILAMENTS WHICH ARE SUBSTANTIALLY FREE OF TWIST AND TWISTING THE CRIMPED FILAMENTS TOGETHER OF A PREDETERMINED STATE OF BULK AND LOOSENESS, THEN COMBINING A PLURALITY OF SUCH COMPONENT STRANDS AND TWISTING THEM TOGETHER WITH LESS TURNS PER UNIT OF LENGHT THAN THOSE OF THE COMPONENT STRANDS AND IN THE DIRECTION OPPOSITE THERETO, SETTING THE YARN IN SAID TWISTED STATE, AND FINALLY SIZING THE YARN. 